1. Field of the Invention
The present invention relates to an acceleration sensor.
2. Description of the Related Art
Methods of this kind are generally known. From published German patent application document DE 197 19 779 A1, for example, an acceleration sensor is known having a seismic mass that is movably suspended on a substrate. In response to an acceleration of the acceleration sensor, inertial forces act upon the seismic mass which deflect the seismic mass relative to the substrate, along a deflection direction. The degree of this deflection is measured using means of detection. The means of detection include a comb electrode structure of electrodes fixed to the substrate and counterelectrodes fixed to the seismic mass, which each extend perpendicularly to the deflection direction, so that along the deflection direction each counter electrode is situated adjacent to a fixed electrode. Between the pairs of counterelectrodes and fixed electrodes functioning as plate capacitors, there form, in each case, electrical measuring capacitances whose contribution is a function of the respective distance between the fixed electrodes and the counter electrodes. In response to a deflection of the seismic mass as a result of an external acceleration acting on the acceleration sensor, the distance changes in each case, and consequently the electrical capacitance between the fixed electrodes and the counterelectrodes. To measure the deflection of the seismic mass, therefore, the changes in the electrical capacitances between the fixed electrodes and the counterelectrodes are evaluated. Based on the electrodes lying opposite to each other along the deflection direction, the acceleration sensor has a comparatively good dynamic air damping. Furthermore, in such an electrode configuration, even a small deflection of the seismic mass leads to a clear capacitance change, and thus to a measuring signal that is able to be evaluated.
Such acceleration sensors are frequently used in the automotive field, for instance, in ESP systems (electronic stability program). In this context, the acceleration sensors are mounted at installation locations at which the acceleration sensors are exposed to comparatively strong vibrations having frequency proportions in the multiple kHz range, such as in the engine compartment. In order that the measuring accuracy is not impaired in this connection, these high-frequency vibrations must not evoke a noticeable measuring signal on the acceleration sensor. It is therefore desirable that the acceleration sensors have a great robustness to vibrations. The robustness to vibration depends, among other things, on the resonant frequency (of the undamped system), so that a lowering in the resonant frequency would lead to an improvement in the robustness to vibration, with respect to higher frequency vibrations. However, lowering in the resonant frequency also leads to an increase in the amplitude of the deflection motion in the case of acceleration. Unfortunately, in the abovementioned known acceleration sensor, only comparatively small deflections are implementable, since otherwise, at low acceleration forces, the measuring signal is too small, and at large acceleration forces there is the danger that an undesired mechanical contact is created between the fixed electrodes and the counterelectrodes. A reduction in the resonant frequency is therefore not possible in the acceleration sensors known from the related art.